The 30 Type CDW Brake Valve, designed and developed by Westinghouse Air Brake Company, is mounted in a locomotive cab and is used by locomotive engineers as a means of initiating a train brake application. When the engineer desires to apply the brakes on a train, the automatic handle of such brake valve is simply pushed forward until the desired brake application has been achieved.
The handle operates through six detented control positions; release, minimum reduction, full service, suppression, handle off and emergency. The service zone is between minimum service and handle off positions. A spring loaded latch provides a positive stop for the handle at each of the six detented positions. The spring loaded latch drops into a cam detent preventing any unintended further brake application or release until the handle is intentionally moved to another position by the engineer.
The force required to move the handle from one detented position to another is important as this is the engineer's safeguard against advancing, or retracting, the automatic handle to an unintended control position and thus affecting the amount of brake applied to the train. Higher than normal handle forces may cause the engineer to believe that a brake application is unavailable resulting in the initiation of an unretrievable brake application from other sources, whereas lower than normal forces may cause the handle to be inadvertently moved to some control position other than the intended position, resulting in undesired braking levels. Therefore, consistent brake valve handle forces are important so that locomotive engineers can expect to apply the same handle force on any locomotive to achieve the desired braking levels.
Current manufacturing methods require that the brake valve latch be assembled into the cam housing with a molybdenum fortified petroleum based grease. The grease is required in order to reduce and control the friction between the latch, latch bushing and cam. Controlling the friction between the mating parts provides for uniform handle forces to move the automatic handle through the various detented control positions. Any lubricant substitution, i.e. the use of a lubricant other than that specified, too little lubricant or the absence of lubricant altogether adversely affects the forces required to move the handle and thus apply the train brakes. Inconsistent handle feel has become a concern to railway engineers and ultimately to railroad management.
Thus, there is a growing need for insuring that the handle forces or handle feel on a railway brake valve be consistent. This consistency is not only important through the detented positions on one brake valve but it is equally important that the handle forces be consistent on the brake valve of any locomotive.